With the development of communication technology, various new radio applications are used depending on preferences or purposes of users. Most radio applications such as LTE, WCDMA, WIMAX, and GSM are executed on a terminal in association with a modem.
To enable such applications to control modems, unique commands of the modems according to modem manufacturers or models should be understood and modules compatible with the commands should be developed. Accordingly, some radio applications are only executed in specific modems or modems of specific manufacturers. To overcome this limitation, all of different commands for various modems are included in an application or different execution files for different modems are produced and distributed.
However, according to such methods, applications should be optimized for each piece of hardware of various commercial modems, and thus it is almost impossible to produce a radio application compatible with all terminals. Moreover, it requires a great amount of human resources to produce a single radio application.
Recently, with the rapid development of wireless communication technology, various communication protocols have been defined. Accordingly, the demand for devices supporting the protocols increases. Radio implementation devices depend on specific hardware such as amplifiers, antennas, and filters to support each protocol, and thus require additional hardware to support new protocols.
Therefore, software-defined radio (SDR) technology for supporting various communication protocols in a single-hardware platform is receiving great attention. The SDR technology aims for openness, interoperability, and portability of a wireless communication system so that the communication system can be compatible with various communication protocols and communication technologies without hardware modification or upgrade.
A conventional single antenna system roughly consists of a modem sub-system and an RF/IF sub-system without considering multiple antennas. Therefore, the conventional single antenna system cannot efficiently adapt to a current rapidly changing communication environment.
A multiple antenna system is receiving great attention since a channel capacity can be increased in proportion to the number of antennas without allocation of additional frequencies or transmission power. In particular, according to multiple-input and multiple-output (MIMO) technology, multiple antennas are used at both transmission and reception sides to increase a channel capacity within limited frequency resources, thereby increasing a data transmission rate. That is, this MIMO technology may remarkably improve data processing capability and a link range without additional bandwidths or transmission power.
However, the multiple antenna system does not have a structure that can be obtained by simply adopting a plurality of single antenna systems supported by an existing SDR system. To support the multiple antenna system, multiple antenna algorithms such as a spatial multiplexing (SM) algorithm, a beamforming algorithm, a space-time coding (STC) algorithm, and a direction of arrival (DOA) estimating algorithm should be provided, and a synchronization issue for the multiple antenna system should be addressed.
According to an SM technique, a virtual sub-channel is established between transmitting and receiving antennas and different data is transmitted through respective transmitting antennas to thereby increase a transmission rate. That is, the SM technique increases a transmission rate using spatial diversity, and is thus suitable for a communication environment in which a fast transmission rate is required.
A beamforming technique is used to allow energy from an antenna to intensively radiate in a specific direction so that a signal is received or transmitted in a desired direction. According to this technique, strength of a signal is adjusted according to position angles of a base station and a mobile station by controlling phase information for each antenna so as to release adjacent interference, thereby improving performance.
An STC technique allows use of a multiple antenna in a wireless communication system so as to improve reliability of data transmission. According to the STC technique, a plurality of overlapping data streams are transmitted so that at least a few of the overlapping data streams are received in a reliable state even when data loss occurs during data transmitting and receiving processes. Thus, the STC technique is suitable for a communication environment in which data reliability is important.
A DOA estimating technique is used to select an antenna beam for transmitting a signal in a desired direction or control an antenna beam of a direction in which a desired signal is received. A beam former estimates steering vectors and DOA for multiple simultaneously detected spatial signals, and determines beamforming weight vectors on the basis of a combination of the steering vectors.
To apply the above-mentioned techniques for multiple antennas to an SDR system, a structure of the SDR system should provide openness, dispersibility, object orientation, and software reusability. An SDR multiple antenna system that satisfies these conditions needs to provide an architecture of a smart antenna sub-system that can be applied to a standard SDR system so as to provide reusability, connectivity, and extendibility.